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. 2021 Jul 6;118(29):e2101783118. doi: 10.1073/pnas.2101783118

Fig. 3.

Fig. 3.

Interference with BMP signaling induces homeotic transformations in dorsal and anal fins. (A–C) Fin morphology of dorsal (A and B) and anal fins (C) in WT (A–C), gremlin1b−/− (A and C), and DMH1-treated (B) fish at approximately 1 mo postfertilization. Bony structures were visualized using Alizarin red (“AZR”), and fins were imaged using fluorescence microscopy. Insets shown (dashed boxes) were taken using brightfield microscopy (“BF”). In A and B, transversal sections at the level of the spine to soft-ray boundary are shown, which in A was imaged using fluorescence microscopy (Alizarin red fluorescence in white) and in B using fluorescence microscopy (Alizarin red fluorescence in false color red) and differential interference contrast microscopy (“DIC”) (in white). The dorsal fins of gremlin1b−/− fish in A show an expanded spine domain (indicated by red line) and reduced soft-ray domain (indicated by blue line) indicating soft-ray to spine homeotic transformations. Alizarin red staining visualizes the heavier ossification of spines as compared to soft rays. Insets show spine (red arrowhead spine tip) and soft-ray (blue arrowhead segment boundary) characters, at the spine to soft-ray transition. Transversal sections through the spine to soft-ray boundary confirm the presence of fused and unfused hemisegments in spines and soft rays, respectively (section position is indicated with circles and numbers). The DMH1-treated fish shown in B show the opposite transformation displaying spine to soft-ray transformations. The Inset shows segments in the most anterior soft ray (blue arrowhead). Transversal sections confirm the presence of unfused soft-ray–like elements in the anterior fin. C shows a comparison of gremlin1b−/− and WT anal fins showing soft-ray to spine transformations. Insets indicate spine and soft-ray characters at the spine to soft-ray boundary. A quantitative analysis of spine and soft-ray counts is provided in SI Appendix, Fig. S5A. (D) Egg spots are present on the soft-ray part of the anal fins of male A. burtoni. In gremlin1b−/−, the egg spots have shifted posterior together with the soft-ray domain. A quantitative analysis of egg spots distribution is provided in SI Appendix, Fig. S5B. AZR: Alizarin red, BF: brightfield, S: spine, SR: soft ray. Anterior is to the left.